1. Technical Field
The present invention relates to a liquid crystal display device employing a polymer-stabilized blue phase liquid crystal.
2. Background Art
Liquid crystal display elements have widely been used in the field of optical information processing. The liquid crystal display system includes various systems of TN, STN, IPS, VA, OCB and so forth, all of which being operated so as to change a preliminarily-controlled alignment of liquid crystal molecules into a different state of alignment by applying an electric field, to thereby change the direction or state of polarization of the transmitted light, and then convert this change into contrast ranging between brightness and darkness while making use of a polarizer plate or the like.
All of these conventional liquid crystal display systems need surface alignment treatment for controlling alignment of the liquid crystal molecules, and in particular those based on the systems other than VA need rubbing. The rubbing is an operation of rubbing the surface of an alignment film, which is formed by coating on the surface of a substrate to be brought into contact with a liquid crystal, using cloth or the like, but is causative of degradation in the yield ratio, consequent rise in the cost, and degradation in quality of display. In addition, the above-described systems make use of nematic liquid crystal, and have achieved a response time of 10 milliseconds or around at the shortest, the performance of which has limited display of movie on television.
In recent years, there have been proposed chiral nematic liquid crystals as the liquid crystal for the liquid crystal display element (Japanese Laid-Open Patent Publication Nos. 2003-295225, 2001-316346 and so forth). Other proposals for solving the above-described problems have been made on use of polymer-stabilized blue phase liquid crystals (Japanese Laid-Open Patent Publication No. 2003-327966, WO2005/090520), in place of the conventional nematic liquid crystals. The polymer-stabilized blue phase liquid crystals are novel materials distinctively expanded in the temperature range allowing therein exhibition of the blue phase, without impairing their rapid response performance. Since the polymer-stabilized blue phase is optically isotropic under the absence of electric field applied thereto, so that there is no need of controlling the alignment. Display is therefore established based on a novel system, making use of phenomena that retardation is not available under the absence of electric field, but is induced under applied electric field. The response time is 100 μs or around, which is distinctively faster than that of the conventional liquid crystal display elements. It is reported also that a desirable contrast may be obtained over a wide range of viewing angle, without causing leakage of light ascribable to retardation in the black state. To achieve a high contrast in the wider-viewing angles by reducing the light leakage caused from the polarizing plates, combing the retardation plate with the liquid crystal cell employing the polymer-stabilized blue phase has been proposed (JPA No. 2005-202383).